Integrated color LED chip

ABSTRACT

A method and apparatus for achieving multicolor displays using an integrated color chip is provided. The integrated color chip contains one or more multicolor generation sites on a single substrate. Each multicolor generation site is comprised of two or more light emitting regions in close proximity to one another, the number of light emitting regions per site dependent upon the number of required colors. The active light generation system for each light emitting region, e.g., an LED, is preferably identical in device structure although size and shape may vary. In order to achieve the desired colors, one or more light conversion layers are applied to individual light emitting regions. Each light emitting region may also include index matching layers, preferably interposed between the outermost surface of the light emitter and the light conversion layer, and protective layers. In order to minimize cross-talk and achieve improved contrast, opaque material is preferably deposited between adjacent light emitting regions. Cross-talk may also be minimized by locating the light emitting regions on a substantially non-reflective substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims benefit from Provisional Application Ser. No.60/214,505, filed Jun. 28, 2000.

FIELD OF THE INVENTION

The present invention relates generally to multicolor display devicesand, more particularly, to a method and apparatus for achieving multiplecolors on an integrated chip.

BACKGROUND OF THE INVENTION

Multicolor generation systems are used in a variety of applicationsincluding monitors (e.g., direct and projection televisions, computermonitors), macro-displays (e.g., billboards), and micro-displays (e.g.,telephones and PDAs). Currently a number of different techniques areused to achieve multicolor displays. For example, depending uponapplication requirements such as contrast, brightness, color range,color accuracy, power consumption, size and cost, a display may utilizelight generation systems based on everything from CRTs to LCDs.

Currently, the emphasis on full-featured microelectronic systems hasresulted in manufacturers working to develop more efficient, multicolordisplays that can replace the simple monotone displays common in suchdevices. Although LCD display based systems have proven adequate forsome applications, device complexity and cost have prohibited their usefor the majority of such systems. The present invention overcomes theobstacles associated with the prior approaches and provides a simpledisplay device that can be tailored to meet varying color and displaysize requirements.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for achievingmulticolor displays using an integrated color chip. The integrated colorchip contains one or more multicolor generation sites on a singlesubstrate. Each multicolor generation site is comprised of two or morelight emitting regions, preferably LEDs, in close enough proximity toone another to achieve color integration. The active light generationsystem for each light emitting region, e.g., an LED, is preferablyidentical in device structure although size and shape may vary. In orderto achieve the desired colors, one or more light conversion layers areapplied to individual light emitting regions. Thus, for example, asimple three color generation site may include three blue light emittingLEDs, one of which includes a blue-to-green light conversion layer andone of which includes a blue-to-red light conversion layer. Each lightemitting region may also include index matching layers, preferablyinterposed between the outermost surface of the light emitter and thelight conversion layer, and protective layers.

The number of required light emitting regions per multicolor generationsite depends upon the application. For example, a two color systemcomprised of a blue color emitting region and a yellow color emittingregion can be used to produce a range of colors, including white.Alternately, a complete color range can be achieved using a three colorsystem comprised of three light emitting regions. Preferably the threelight emitting regions in combination with the required light conversionlayers emit three primary additives such as red light, green light, andblue light.

In at least one embodiment of the invention, opaque material isdeposited between adjacent light emitting regions thereby minimizingcross-talk and achieving improved contrast. In at least one otherembodiment of the invention, cross-talk due to substrate reflections isminimized by removing the light emitting regions from the substrate onwhich they were grown and affixing them to a secondary, supportsubstrate. In at least one other embodiment of the invention, cross-talkdue to substrate reflections is minimized by interposing an absorbing orpartially reflective material between the substrate and the lightemitting regions.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an embodiment of the invention comprised of athree color integrated color chip;

FIG. 2 is a top view of an alternate embodiment of the invention with animproved emitter packing density;

FIG. 3 is a top view of an alternate embodiment of the invention inwhich the light emitting regions are of different dimensions tocompensate for variations in perceived light intensity;

FIG. 4 is a cross-sectional view of an embodiment of the invention;

FIG. 5 is a cross-sectional view of an alternate embodiment of theinvention;

FIG. 6 is an illustration of an integrated color chip containing aplurality of multicolor sites;

FIG. 7 illustrates cross-talk between adjacent light emitting regions;

FIG. 8 illustrates one method of isolating adjacent light emittingregions;

FIG. 9 is a cross-sectional view taken along plane A—A of the embodimentshown in FIG. 8;

FIG. 10 is a cross-sectional view of an alternate method of minimizingcross-talk due to edge emissions;

FIG. 11 is a cross-sectional view of an embodiment of the inventiondesigned to minimize cross-talk due to light emitted into the substrate;

FIG. 12 illustrates the first stage of an alternate approach tominimizing cross-talk between the individual light emitting regions ofthe invention;

FIG. 13 illustrates the second stage of an alternate approach tominimizing cross-talk between the individual light emitting regions ofthe invention;

FIG. 14 illustrates the third stage of an alternate approach tominimizing cross-talk between the individual light emitting regions ofthe invention; and

FIG. 15 illustrates the fourth stage of an alternate approach tominimizing cross-talk between the individual light emitting regions ofthe invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is an illustration of an embodiment of the invention. In theembodiment shown, an integrated color chip (ICC) 100 contains a singleset of color emitting regions 101-103 residing on a single substrate 105(e.g., a substrate comprised of sapphire, silicon carbide, galliumnitride, etc.). Preferably light emitting regions 101-103 are insufficiently close proximity to one another to facilitate colorintegration by an observer. It will be understood that as the apparentdistance between ICC 100 and the observer increase, the required spacingbetween light emitting regions 101-103 increases. Although each lightemitting region 101-103 is illustrated as having a circular shape, it isunderstood that the inventor envisions other shapes. For example, asshown in FIG. 2, light emitting regions 201-203 are non-circular inorder to achieve improved packing density. Alternately, as shown in FIG.3, light emitting regions 301-303 are of different dimensions, thedimensional variations compensating for variations in perceived lightintensity from the different emitting regions, thus achieving a balancedoutput.

In the preferred embodiment of the invention, each individual lightemitting region (e.g., regions 101-103, 201-203, and 301-303) iscomprised of a light emitting diode (LED) and, as required to achievethe desired color, a color (i.e., wavelength) conversion layer (e.g.,one or more phosphor and/or active polymer layers). Preferably the LEDsemit violet or blue light (i.e., in the wavelength range of between4,000 and 4,912 Angstroms) although it is understood that the inventioncan utilize other wavelength LEDs. The LED structures can bemanufactured using a variety of fabrication techniques that are wellknown by those of skill in the art. In the preferred embodiment of theinvention, the LED structures are grown on substrate 105 using the BVPEtechniques disclosed in pending U.S. patent application Ser. No.09/861,011, pages 7-15, the teachings of which are hereby incorporatedby reference. However, other device manufacturing techniques such asMOCVD and MBE can also be used to fabricate the LED structures of thepresent invention.

Assuming that the LED structures emit blue light, only two of the threelight emitting regions require color conversion layers in order toachieve a tristimulus color space that can be used to generate anydesired color. For example and as illustrated in FIG. 4, by applying aconversion layer 401 to light emitting region 101 to down frequencyconvert the emitted blue light to green light (i.e., in the wavelengthrange of between 4,912 and 5,750 Angstroms), and applying a conversionlayer 403 to light emitting region 103 to down frequency convert theemitted blue light to red light (i.e., in the wavelength range ofbetween 6,470 and 7,000 Angstroms), the standard set of additiveprimaries can be generated (i.e., red, green and blue or RGB). It isunderstood that the invention can also be used to generate non-RGB lightemissions for a variety of applications, some of which do not requirethe ability to generate all colors. For example, the invention can beused to generate a subset of the visible colors with only two lightemitting regions.

The light converting coatings, for example blue-to-green layer 401 andblue-to-red layer 403, are preferably deposited onto the designatedlight emitting regions using standard coating techniques as are wellknown by those of skill in the art. For example, the first conversionlayer (e.g., layer 401) can be deposited by spraying or spin coatingfollowed by a curing step. Once cured, the coating is selectivelyremoved by standard photolithographic techniques so that onlypredetermined light emitting regions (or region for a structurecomprised of only three light emitting regions) are covered by theconversion layer. The same process is then used to coat the secondconversion layer (e.g., layer 403). It is understood that a variety ofother well known techniques can be used to deposit the desired lightconversion layers. For example, a masking system can be used toselectively coat predetermined light emitting regions, the maskingsystem used in conjunction with a liquid, evaporative, or other coatingtechnique. Alternately, an automated, microrobotic drop dispenser can beused to deposit the conversion layers on each of the designated lightemitting regions.

Preferably an index of refraction matching layer 501 is interposedbetween light emitting region 101 and light converting coating 401 andan index of refraction matching layer 503 is interposed between lightemitting region 103 and light converting coating 403 as illustrated inFIG. 5. Matching layers 501 and 503 are selected from a class oftransparent materials having an index of refraction between that of theunderlying semiconductor material and that of the overlying lightconversion coating. The matching layers facilitate the definition of theconversion layers by planarizing or partially planarizing the lightemitting regions prior to the application of the conversion layers.Matching layers 501 and 503 are preferably deposited using the sametechniques used to deposit the conversion layers, thus simplifying thefabrication process.

In some embodiments of the invention, a protective layer 505 isdeposited onto the device. Protective layer 505 provides anenvironmental sealant for the device and, more particularly, for theconversion layers. Additionally, layer 505 is preferably designed toprovide an index of refraction matching layer to the ambient environment(e.g., air) and to provide lensing to converge the emitted light raysand project them away from the device's surface. As shown in FIG. 5,protective layer 505 covers all three light emitting regions although itis understood that the protective layer can be deposited on only aportion of the device structure (e.g., only on the light conversionlayers). Preferably protective layer 505 is deposited using the sametechniques as used with the conversion layers, thus simplifying thefabrication process.

In the preferred embodiment of the invention, a first contact 507 islocated on the lower surface of substrate 105. A second contact isdeposited on the upper surface of each light emitting region prior tothe application of the index matching layers (e.g., 501 and 503), lightconversion layers (e.g., 401 and 403), and/or any protective layers(e.g., 505). In the illustrated embodiment, contact 508 corresponds tolight emitting region 101, contact 509 corresponds to light emittingregion 102, and contact 510 corresponds to light emitting region 103.

A variety of techniques can be used to connect to the contacts locatedon the upper surfaces of the emitting regions. For example, after all ofthe desired coating layers are applied to the light emitting regions, aphotoresist mask can be used in conjunction with an etching system toexpose bonding areas (e.g., bonding pads) on each of the contacts (e.g.,contacts 508-510). Alternately, laser ablation can be used to removeportions of the coating layers, thereby exposing bonding areas.Alternately, leads can be coupled to the contacts prior to theapplication of the coatings. Alternately, wrap-around contacts can beapplied such that a portion of the contact wraps-around the edge of thelight emitting regions. Leads can be coupled to the edge contacts priorto the application of the coatings or after subsequent exposure of theedge contacts by an etching or ablation technique. Alternately, afterdeposition of an insulating layer over the entire ICC and exposure of abonding area on each contact, leads can be coupled to the contacts andconnected to bonding regions on the edges of the ICC. In someembodiments, the insulating layer also acts as the index matching layerinterposed between the light emitting regions and the light conversionlayers. In other embodiments, the insulating layer is interposed betweenthe light emitting regions and the index matching layer.

It is understood that the above-identified embodiments, for example theconfigurations illustrated in FIGS. 1-3, are meant to be illustrative,and not limiting, of the invention. For example, the ICCs illustrated inthese figures include only three light emitting regions per substrate.FIG. 6 illustrates a preferred embodiment of the invention in which asingle substrate 601 includes a plurality of multicolor generation sites603. Preferably each multicolor generation site 603 is comprised ofthree individual light emitting regions, at least two of which use colorconversion layers as previously described, although it is understoodthat each multicolor generation site 603 may be comprised of eitherfewer or greater numbers of individual light emitters. Additionally, itis understood that not all of the multicolor generation sites on asingle substrate must be comprised of an equivalent number of individuallight emitters.

Although the above-described embodiments provide multiple colors,improved contrast can be achieved by suppressing cross-talk betweenindividual light emitting regions. The cross-talk phenomenon isillustrated in the cross-sectional view of a simplified device 700provided in FIG. 7. As shown, two adjacent light emitting regions 701and 703 are contained on a single substrate 105. Light emitting region701 includes a light conversion layer 705 and light emitting region 703includes a light conversion layer 707. At a given time x, light emittingregion 701 is activated. In addition to the light 709 emitted from theupper surface of 701, which passes through conversion layer 705,additional light is emitted from the side of region 701 (e.g., light711) as well as the bottom surface of region 701 (e.g., light 713). Aportion of the side emitted light 711 and, to a lesser extent, bottomemitted light 713, may pass through adjacent region 703 and/orconversion layer 707. As a result, when one light emitting region isactivated (e.g., 701) a portion of unintended light is emitted by theadjacent region (e.g., 703).

In an embodiment of the invention illustrated in FIG. 8, a plurality ofmulticolor sites 801, each comprised of three light emitting regions803, is grown/deposited on a single substrate 805. It is understood thatpreferably adjacent light emitting regions 803 utilize different colorconversion layers in order to achieve the desired multicolor system asdescribed above. In the embodiment of the invention illustrated in FIG.8 and further illustrated in FIG. 9, individual light emitting regions803 are isolated from adjacent regions with an opaque material 807(e.g., low temperature glass, epoxy, or any of a variety of opaqueorganic materials). Opaque material 807 can be deposited, for example,using standard photolithographic coating techniques or any of a varietyof other well known techniques such as a masking system used inconjunction with a liquid, evaporative, or other coating technique. Inan alternate embodiment of the invention illustrated in FIG. 10,channels 1001 are formed between the light emitting regions, for exampleusing an ion etching or plasma etching system, prior to filling in thechannels with opaque material 807.

Although the embodiments illustrated in FIGS. 8-10 aid in theelimination of cross-talk resulting from edge emissions, theseembodiments do not significantly impact cross-talk arising from lightemitted into substrate 805 (e.g., light 713 shown in FIG. 7). Oneapproach to minimizing cross-talk due to light emitted into thesubstrate is illustrated in FIG. 11. As shown, a layer 1101 is grown ordeposited on the surface of substrate 1103 prior to the growth of lightemitting regions 1105. Layer 1101 can be designed to be substantiallyabsorbing, opaque, or reflective to certain wavelengths in order tominimize undesired substrate reflections. For example, layer 1101 can bea distributed Bragg reflector, preferably comprised of a three regionstack optimized for the three wavelengths of interest (e.g., red, greenand blue light). Preferably, as in the prior example, the area betweenadjacent regions 1105 is filled with opaque material 807. It isunderstood that light emitting regions 1105 include, as previouslydescribed, light conversion layers as required to achieve the desiredwavelengths, contact structures, protective coatings (if desired) andindex matching layers (if desired).

FIGS. 12-15 illustrate an alternate approach to minimizing cross-talkbetween light emitting regions. During the first stage of devicefabrication, illustrated in FIG. 12, light emitting regions 1201 aregrown on substrate 1203. The order of the layers (e.g., the n-type andp-type layers) comprising regions 1201 is reversed from the desiredfinal order. During the second stage of device fabrication, illustratedin FIG. 13, opaque material 1301 is deposited between adjacent regions1201 in order to isolate the edges of the emitting regions.Additionally, the top surfaces of regions 1201 are coated with a contactlayer 1303. Preferably contact layer 1303 is comprised of metal and isopaque to visible light, and more preferably reflective of visiblelight. During the third stage of device fabrication, illustrated in FIG.14, a second substrate 1401 is coupled to the top surfaces of regions1201, preferably via interposed contact layers 1303. The couplingsurface of substrate 1401 may be conductive, thus allowing voltage to besimultaneously applied to one surface (e.g., contact layer 1303) of allemitting regions 1201. Alternately, substrate 1401 may include aplurality of leads that correspond to individual regions 1201 (e.g.,individual contact layers 1303), thus allowing voltage to be appliedselectively to regions 1201. In the last stage of device fabrication,illustrated in FIG. 15, substrate 1203 is removed, for example by usingan etching or ultraviolet laser heating technique. After exposure ofregions 1201, suitable light conversion layers 1501 are applied asdescribed above. Additionally, index matching layers, protective layers,and contact structures are applied as described above.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof Accordingly, thedisclosures and descriptions herein are intended to be illustrative, butnot limiting, of the scope of the invention which is set forth in thefollowing claims.

What is claimed is:
 1. A multicolor display comprising a substrate; andat least one multicolor generation site coupled to said substrate, eachof said at least one multicolor generation sites comprised of: at leasttwo light emitting regions proximate to one another; and at least onewavelength conversion layer applied to at least one of said at least twolight emitting regions, wherein said at least two light emitting regionsin combination with said at least one wavelength conversion layer emitat least two different colors; and a cross-talk minimization layerinterposed between said substrate and said at least two light emittingregions.
 2. A multicolor display comprising a substrate; and amulticolor generation site grown on said substrate comprising: at leasttwo LEDs proximate to one another; and a first wavelength conversionlayer applied to a light emitting surface of a first of said at leasttwo LEDs, wherein said at least two LEDs in combination with said firstwavelength conversion layer emit at least two different colors; and across-talk minimization layer interposed between said substrate and saidat least two LEDs.
 3. The multicolor display of claim 2, wherein said atleast two LEDs are comprised of three individual LEDs proximate to oneanother.
 4. The multicolor display of claim 3, further comprised of asecond wavelength conversion layer applied to a light emitting surfaceof a second of said three individual LEDs, wherein said three individualLEDs in combination with said first and second wavelength conversionlayers emit three different colors.
 5. The multicolor display of claim2, wherein said at least two LEDs emit light at a wavelength in therange of wavelengths between 4,000 and 4,912 Angstroms.
 6. A multicolordisplay comprising a substrate; and a plurality of multicolor generationsites grown on said substrate, each of said plurality of multicolorgeneration sites comprised of: at least two LEDs proximate to oneanother; and a wavelength conversion layer deposited on a light emittingsurface of a first of said at least two LEDs, wherein said at least twoLEDs in combination with said wavelength conversion layer emit at leasttwo different colors; and a cross-talk minimization layer interposedbetween said substrate and said at least two LEDs.
 7. The multicolordisplay of claim 6, further comprising an index matching layerinterposed between said wavelength conversion layer and said lightemitting surface of said first LED.
 8. The multicolor display of claim6, further comprising a protective layer deposited on an exteriorsurface of said wavelength conversion layer.
 9. The multicolor displayof claim 6, further comprising a protective layer deposited on a lightemitting surface of a second of said at least two LEDs.
 10. Themulticolor display of claim 6, further comprising a region of opaquematerial deposited between said at least two LEDs.
 11. The multicolordisplay of claim 6, wherein said substrate is selected from the groupconsisting of sapphire, silicon carbide and gallium nitride.
 12. Themulticolor display of claim 6, wherein said at least two LEDs emit lightat a wavelength in the range of wavelengths between 4,000 and 4,912Angstroms.
 13. The multicolor display of claim 6, wherein saidcross-talk minimization layer is comprised of a Bragg reflector.
 14. Themulticolor display of claim 6, wherein said cross-talk minimizationlayer is comprised of a partially absorbing layer.
 15. A multicolordisplay comprising a substrate; and a plurality of multicolor generationsites grown on said substrate, each of said plurality of multicolorgeneration sites comprised of: three LEDs proximate and immediatelyadjacent to one another; a first wavelength conversion layer depositedon a light emitting surface of a first of said three LEDs; and a secondwavelength conversion layer deposited on a light emitting surface of asecond of said three LEDs, wherein said three LEDs in combination withsaid first and second wavelength conversion layers emit three differentwavelengths; and a cross-talk minimization layer interposed between saidsubstrate and said three LEDs.
 16. The multicolor display of claim 15,wherein said substrate is selected from the group consisting ofsapphire, silicon carbide and gallium nitride.
 17. The multicolordisplay of claim 15, wherein said first and second wavelength conversionlayers are selected from the group of materials consisting of phosphorsand active polymers.
 18. The multicolor display of claim 15, whereinsaid three LEDs emit light at a wavelength in the range of wavelengthsbetween 4,000 and 4,912 Angstroms.
 19. The multicolor display of claim15, wherein said first wavelength conversion layer converts light in afirst wavelength range of between 4,000 and 4,912 Angstroms to light ina second wavelength range of between 4,912 and 5,750 Angstroms.
 20. Themulticolor display of claim 15, wherein said second wavelengthconversion layer converts light in a first wavelength range of between4,000 and 4,912 Angstroms to light in a second wavelength range ofbetween 6,470 and 7,000 Angstroms.
 21. The multicolor display of claim15, further comprising: a first index matching layer interposed betweensaid first wavelength conversion layer and said light emitting surfaceof said first LED; and a second index matching layer interposed betweensaid second wavelength conversion layer and said light emitting surfaceof said second LED.
 22. The multicolor display of claim 15, furthercomprising: a first protective layer deposited on an exterior surface ofsaid first wavelength conversion layer; and a second protective layerdeposited on an exterior surface of said second wavelength conversionlayer.
 23. The multicolor display of claim 22, wherein said first andsecond protective layers are equivalent layers.
 24. The multicolordisplay of claim 22, further comprising a third protective layerdeposited on a light emitting surface of a third of said three LEDs. 25.The multicolor display of claim 15, further comprising a region ofopaque material deposited between adjacent surfaces of said three LEDs.26. The multicolor display of claim 15, further comprising: a pluralityof channels within said substrate, said plurality of channels separatingadjacent LEDs of said three LEDs; and opaque material deposited withinsaid plurality of channels.
 27. The multicolor display of claim 15,wherein said cross-talk minimization layer is comprised of a Braggreflector.
 28. The multicolor display of claim 15, wherein saidcross-talk minimization layer is comprised of a partially absorbinglayer.